This project involves the rigorous physical measurement of the immediate and long-range morphologic changes associated with orthodontic treatment of Class II malocclusion. Our intention is to measure and described the changes which typically occure during and after treatment: (a) in the conformation of the skull and jaws; (b) in the positional relationships of the teeth; (c) in the thickness and contour of the facial and pharyngeal soft tissues. Our treatment is intended to reflect both the range of conditions coventionally grouped in the diagnostic category, "Class II malocclusion," and the range of currently accepted types of treatment. It also includes a control group of untreated subjects with Class II malocclusions, permitting parallel evaluation of the natural course of developmental change for such subjects through time. A machine-readable numerical data base is being constructed which contains data encoded from measurement of x-ray films and study casts. These data are secured through previously developed computer-aided methods which incorporate well-tested error detection algorithms. A complementary rapidly accessible graphics data base is also being developed consisting of microfiche images of the same x-ray films and study cast photographs from which the numerical data are obtained. The ability to cycle rapidly between the visual and the numerical data leads to improved understanding of their meaning, especially in cases where real outlying numerical values exist for key variables. The accumulated data are used for computer-conducted hypothesis-testing experiments whose general aim is to test the goodness of extant orthodontic theory in explaining the observed effects of treatment so as to facilitate the development of better theories and better methods of treatment.